Metal material is now being widely used in the field of medical treatment. For instance, stainless steel is used for stent, and titanium particles are used for joints of artificial heart. Although these metal materials are mechanically strong and are handleable, they have a grave defect that, when brought into contact with blood, they activate blood to cause thrombus. Therefore serious side effects like cerebral infarction have been sometimes brought about. Hence, various studies have been made to develop medical technique by which to process the surface of these metal materials, to prevent coagulation reaction which occurs owing to the activation of blood, and to thus give antithrombotic properties to metal materials. Fundamental solution has however yet to be achieved.
Paying attention to the fact that active oxygen plays an important role in the activation of blood, the inventors of this invention have so far reported that a polymer which has nitroxylradical which gets rid of active oxygen, when applied to living body, can be used for the treatment of various species of inflammation or the like (Patent Document 1), or that said polymer can be used for the improvement of biocompatibility of a surface which gets in contact with substance which is originated from living body (Patent Document 2). They have also reported that polystyrene beads coated with said polymer inhibit the activation of blood (Non-patent Document 1). Furthermore, the inventors of this invention have developed a technique by which to coat a metal surface with polymer having phosphoric acid residue (Non-patent Document 2).
There has been a demand in medical field for the development of a new material for stent or the like which has antithrombotic properties. In response, there has been developed medical agent-eluting stents which have on their surface a medical agent having antithrombotic properties. There are reports, however, that these stents are more likely to cause thrombus to some patients as compared with conventional stents. Long period effects of those stents are yet to be verified. It is expected therefore that a metal material which maintains mechanical advantages and can also give antithrombotic properties would be able to be applied not only to stent but also to other devices made of metal.